1. Field of the Invention
The present invention relates generally to radio communication system technologies, and more particularly, to a method and apparatus for transmitting Hybrid Automatic Repeat reQuest ACKnowledgment (HARQ-ACK) feedback information.
2. Description of the Related Art
A Long Term Evolution (LTE) system supports two duplexing modes, i.e., Frequency Division Duplexing (FDD) and Time Division Duplexing (TDD).
FIG. 1 illustrates a frame structure of a conventional TDD system.
Referring to FIG. 1, a length of each radio frame is 10 ms, and each radio frame is divided into two 5 ms half-frames. Each half-frame includes eight 0.5 ms time slots and three special fields, i.e., a Downlink Pilot Time Slot (DwPTS), a Guard Period (GP), and an Uplink Pilot Time Slot (UpPTS). The total length of the three special fields is 1 ms.
Each subframe includes two consecutive time slots. For example, a frame k includes slot 2k and slot 2k+1.
The TDD system supports seven TDD uplink/downlink configurations, as shown in Table 1 below. In Table 1, D denotes a downlink subframe, U denotes an uplink subframe, and S denotes a special subframe with the above-mentioned three special fields.
TABLE 1Index Switching number ofpointindex of subframeconfigurationperiod012345678905msDSUUUDSUUU15msDSUUDDSUUD25msDSUDDDSUDD310msDSUUUDDDDD410msDSUUDDDDDD510msDSUDDDDDDD610msDSUUUDSUUD
To improve a user transmission rate, an LTE-Advanced (LTE-A) system has been proposed. In LTE-A, multiple Component Carriers (CCs) are aggregated to obtain greater bandwidth, i.e., Carrier Aggregation (CA), which constitutes a downlink and an uplink of a communication system to support a higher transmission rate. For example, a 100 MHz bandwidth may be achieved by aggregating five 20 MHz CCs. Herein, each CC may be referred to as a Cell.
A Base Station (BS) may configure a User Equipment (UE) to work in multiple CCs, one of which is a primary CC (PCC or Pcell), while any other CCs are a secondary CC (SCC or Scell).
In the LTE-A system, all of the CCs aggregated together are configured with an FDD configuration or are all configured with a TDD configuration.
However, to further improve a user transmission rate, subsequent research is being performed on LTE-A in the hopes of determining a method to effectively support a CC configured with a TDD configuration and a CC configured with a FDD configuration to perform carrier aggregation. For example, when carrier aggregation includes a CC configured with a TDD configuration and a CC configured with a FDD configuration, the is no current way for a UE to determine a HARQ-ACK timing for transmitting HARQ-ACK.